Oil Filtration Requirements for Industrial Servo Systems

The most effective way to reduce life cycle costs of an oil hydraulic system, regardless of the types of valve used, is through close attention to contamination control. There is a wide range of information on the subject so we are summarizing the key concepts.

For industrial servo systems the ideal system filter arrangement is summarised as follows:

  • Use a 15 micron (Beta 15 >= 75) high pressure filter without by-pass just before the valve or critical parts of the valve (e.g. pilot)
  • Use a 3 micron (Beta 3 >= 75) low pressure filter in the return or bypass line.
  • Use a filter in the tank breather that is at least the same filtration level as the finest filter in the system.

This recommendation is based on the fact that most servo and proportional valves can accept the odd particle up to 25 microns so the pressure filter will protect the valve from catastrophic failure. The real work is done by the low pressure filter reducing the small particle contamination which is the prime contributor to component wear and silting.

Assuming that the filters are properly dimensioned and care is taken during initial installation and maintenance the aim should be to limit oil contamination to 16/13 (under the old ISO 4406) or 19/16/13 (under the new ISO 4406). For long life, the maximum levels per the old and new ISO are 15/12 and 18/15/12, respectively. This may

It is important to note that these are maximum contamination levels and with proper care and regular filter change significantly lower levels can and should be achieved. Also attention must be paid to a number of other factors that contribute to oil condition problems such as elevated temperatures, high tank humidity, “dirty” new oil etc.